ルイスオサムシの繁殖様式と発育零点

Abstract

A ground beetle, Carabus lewisianus Breuning, inhabiting woodlands in Izu peninsula, was studied to determine its reproductive phenology. Adults were collected by pitfall traps and dissected to determine their reproductive status. The lower development threshold (T0) and the thermal constant (K) were estimated for egg development. Overwintered adults appeared in late April. No gravid females were found after mid-September. Three peaks were observed in May, June and August during the beetle catches, and each seemed to correspond with the first, second and third oviposition activities of overwintered females, respectively. The expected per capita fecundity was estimated to be less than 50 eggs. The values of T0 and K for eggs were 6.36°C and 133.3 dd using the conventional method, and 7.86°C and 120 dd using Ikemoto and Takai's method. K values from egg to adult were estimated assuming isomorphy, so that the egg period accounted for 18% of the total developmental period. Based on the common temperature of development, i.e. 15–16°C, this species may have originated in a temperate area. Although the total available effective temperature from May to August was sufficient to allow two complete generations, this species reproduced by only one generation a year due to reproductive diapause.